Abstract
OBJECTIVE: Among individual depressive symptoms, anhedonia has been reliably associated with activation of the innate immune response. However, it is unclear whether this association extends to T cell cytokines and if gender differentially affects this association. METHOD: Concentrations of T (IL-17, T-helper (Th) 1- and Th2-) and non-T cell cytokines were measured in plasma using the Bioplex Pro™ human cytokine multiplex kit in Combining Medications to Enhance Depression Outcomes (CO-MED) trial participants who provided plasma at baseline (n = 166). Anhedonia was measured with three items of the clinician-rated Inventory of Depressive Symptomatology and depression severity (minus anhedonia item) was measured with Quick Inventory of Depression Severity Self-Report version (modified-QIDS-SR). Separate generalized linear models for anhedonia and modified-QIDS-SR as dependent variables were conducted with IL-17, Th1-, Th2-, and non-T cell- cytokines as primary independent variables and gender, body mass index (BMI), and age as covariates. Exploratory analyses included gender-by-biomarker interactions. RESULTS: Higher levels of IL-17 (p = 0.032), Th1- (p = 0.002), Th2-(p = 0.001) and non-T-(p = 0.009) cell markers were associated with greater severity of anhedonia controlling for BMI, age, and gender. Gender also had a significant main effect on anhedonia, however, there was a significant gender by immune marker interaction only for IL-17 (p = 0.050). Anhedonia severity increased with higher IL-17 in males (r = 0.42, p = 0.003) but not in females (r = 0.09, p = 0.336). Only non-T cell markers were associated with the modified-QIDS-SR, and there were no significant gender-specific associations with this variable. CONCLUSIONS: T and non-T cell-related inflammatory markers were associated with greater severity of anhedonia, while gender moderated the association of IL-17 with anhedonia in patients with major depressive disorder.